1. Field of the Invention
This invention relates to a safe and simple method for treating a catalyst used for the catalytic reaction of hydrocarbons when the catalyst is removed from the reaction system.
2. Description of the Prior Art
In general, the catalysts used in the catalytic reaction of hydrocarbons such as naphtha, kerosene, gas oil or atmospheric residual oil are deactivated by catalyst poisons or coke deposits formed during the reaction. It therefore becomes necessary to remove the deactivated catalyst from the reactor and exchange it with a fresh catalyst on such occasions. However, the waste catalyst from the catalytic reaction of atmospheric residual oil is in the form of a hard cake which must be crushed mechanically before removal. A dust of the pulverized waste catalyst is generated as a result of, for example, impact at the time of removal, and the dust markedly affects the working environment. Furthermore, when the waste catalyst is removed into the atmosphere, the adhering matter is oxidized by oxygen in the air to generate heat, which in turn causes the adhering matter on the waste catalyst to burn, resulting in a spontaneous combustion of the waste catalyst.
Many attempts have been made to solve the problems involved in the removal of waste catalysts. Two recent proposals are (1) the circulation of an organic amine-containing mineral oil through the reactor to thereby clean and soften a hard cake of waste catalyst (Japanese Patent Publication No. 50033/77 corresponding to U.S. Pat. No. 4,155,875) and (2) wetting the waste catalyst with water or mineral oil in the presence of a surfactant alone or in combination with a chelating agent (Japanese Patent Publication No. 44755/77 corresponding to U.S. Pat. No. 4,031,031). Both methods either soften or wet a hard cake of waste catalyst and therefore are effective for preventing the formation of fines during removal and the hazardous spontaneous combustion. However, the removal of a hard catalyst cake that results from direct desulfurization of atmospheric residual oil requires a two-stage treatment wherein the cake is first softened by the method (1) and then wetted by the method (2). Moreover, one problem with this two-stage treatment is that part of the organic amine used in the method (1) is decomposed and forms ammonia and odorous lower amines which are detrimental to the working environment. Another problem is that the mineral oil used in the treatment must be deodorized before reuse.